1. Field of the Invention
The present invention relates generally to improvements in guide bars for chain saws, and more particularly pertains to improvements in the design to an idler roller used in the free end of a chain saw guide bar.
2. Discussion of the Prior Art
It is currently standard practice in the prior art to use an idler sprocket in the free end of a chain saw guide bar, which is a sprocket wheel journaled on a bearing plate (or ring) by a roller (or ball) bearing. The prior art has also used an idler roller, a round wheel journaled on a bearing plate (or ring) by a roller (or ball) bearing to lift the side links, of a currently popular type of endless saw chain comprised of center drive links and laterally opposed side links, off the guide bar rails by supporting the drive links as the saw chain travels around the free end of the chain saw guide bar.
An idler roller is much preferred to an idler sprocket because it results in the generation of much less friction during operation, generating less heat, and providing a faster chain speed and faster cutting. Moreover, a single roller is usable with a wide range of chains of different pitch, whereas an idler sprocket must be designed for a particular pitch of chain. However, idler rollers of current design are prone to frequent failure. The present invention provides a design for an idler roller used in the free end of a chain saw guide bar which prevents these typical modes of failure in prior art idler rollers.
Currently, two typical constructions exist for supporting an idler roller within flat parallel nose plates on the free end of a chain saw guide bar:
1. The nose plates are formed by being left when the recess is machined into a solid one piece guide bar; or PA1 2. The nose plates are formed by the outer two laminations of a laminated guide bar or laminated nose assembly attached to a solid one piece guide bar. PA1 1. Within the free end of the guide bar, outwardly extending impressions are formed in each of the side nose plates, allowing the use of an idler roller of greater thickness than could be used in the normal prior art gap between parallel nose plates. PA1 2. A groove is machined in the outer circumference of the idler roller in which the drive links of the chain track, stopping the chain from wearing a path down between the idler roller and one of the side nose plates.
In previous prior art designs, the thickness of the idler roller was limited by the gap between the nose plates at the point where the drive links enter the nose, because the nose plates were flat and parallel. This limitation allowed the drive links, after considerable wear, to force their way down between the toothless idler roller and one of the side plates, hence jamming rotation of the idler roller and causing premature failure of the guide bar.